Cation Distribution and Temperature Dependence of Brillouin Function for Nickel-Substituted Manganese–Zinc Ferrites

Ni-substituted manganese-zinc (MnZn) ferrites with the composition of Mn_0.506-xZn_0.244Ni_xFe_2.250O_4.0 (x = 0.066~0.122) have been prepared by the solid-state reaction method. The cation distribution has been investigated by the Rietveld refinement of X-ray diffraction patterns, the microstructure has been observed using a scanning electron microscope, and the magnetic property has been measured using superconductor quantum interference devices and B-H analyzer. The results show that Zn²⁺ and Ni²⁺ ions prefer to occupy the tetrahedron site (A sublattice) and octahedron site (B sublattice), respectively. However, Mn²⁺ and Fe³⁺ ions can enter into A and B sublattices, where the ratio of Mn²⁺ ions occupying A and B sublattices is 4:1. The lattice parameter (a) of the samples decreases with the increase of Ni-substituted content. Meanwhile, based on the Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients ω_AA, ω_BB, and ω_AB of the Ni-substituted MnZn ferrites have been calculated, and the magnetic moment of A and B sublattices versus temperature T has also been investigated. The fitting results match well with the experimental data. Both ω_AB and ω_BB increase with the increase of the Ni-substituted content, but ω_AA shows the opposite variation trend. The Curie temperature also increases with the increasing of the Ni-substituted content, which is attributed to the enhancement of superexchange interaction for A-B sublattice. In addition, the temperature dependence of initial permeability and core loss has been discussed.